Chemical Constituents of the Stem Bark of the Hybrid Plant Citrus × paradisi Macfad. (Rutaceae)

The stem bark of Citrus × paradisi Macfad. (Rutaceae) gave (23S)-isolimonexic acid (1), limonin (2), citracridone II (3), citpressine II (4), citpressine I (5), grandisine (6), 2-hydroxynoracronycine (7), citracridone I (8), 5-methoxyseselin (9), umbelliferone (10), scopoletin (11), naringenin (12), apigenin (13), friedelin (14), agrostophyllinone (15) and stigmasterol-3-O-β-D-glucopyranoside (16). The structures of the compounds were determined using NMR and MS spectroscopic data, and by comparison with published data. The relative configuration of 1 was proposed as (23S)-isolimonexic acid using NOE studies. Hydrogenation reaction of compound 3 led to the new derivative 3',4'-dihydrocitracridone II (3a). Cytotoxicity activities against the human adenocarcinoma alveolar basal epithelial cell lines A549 and the Caucasian prostate adenocarcinoma cell lines PC3, using the MTT assays showed that the methanol crude extract was significant with IC₅₀ values of 30.1 and 31.7 μg/mL, respectively, with the positive control, doxorubicin giving an IC₅₀ of 0.9 μM. In addition, compounds 3, 7 and 8 gave moderate cytotoxic activities with IC₅₀ values of 33.1, 31.2 and 32.5 μM for A549 cells and 35.7, 33.8 and 34.9 μM for PC3 cells, respectively. The hydrogenated 3a was less active than 3, suggesting that the presence of the double bond in pyrans is important for structure-activity relationship.

Management of the Citrus Nematode, Tylenchulus semipenetrans

Of the many nematode species that parasitize citrus, Tylenchulus semipenetrans is the most important on a worldwide basis. Management of the citrus nematode remains problematic as no one tactic gives adequate control of the nematode. An overall management strategy must include such components as site selection, use of non-infected nursery stock, use of at lease one post-plant nematode control tactic, and careful management of other elements of the environment that may stress the trees. Nematicides continue to play a key role in management of this pest. Optimum results require careful attention to application techniques.